The most pertinent prior art of which applicants are aware is the allowed copending application U.S. Ser. No. 07/226,634, filed Aug. 1, 1988, which discloses a method and circuitry employing a signal feed-forward technique for suppressing additive transient disturbances in a data channel. Such disturbances may be due to thermal asperity transients caused by an MR transducer contacting a moving storage surface.
This prior art method and circuitry operates satisfactorily when, as in the case of the just-described thermal asperity transient, the additive disturbances of the analog input signal are monopolar; i.e., the disturbances are known in advance to be of either positive or negative polarity. In other words, the circuitry is unable to accommodate additive transient disturbances that at one time may be of positive polarity and at other times of negative polarity. This is due, in part, to the so-called "peristaltic" connection required for positive/negative envelope detection. This prior method and circuitry employs essentially a feed-forward approach wherein branch gains are critical. Also this prior method, as disclosed, operates best only when the additive disturbance has at most one time constant associated with the decay.
Other prior art of incidental interest includes U.S. Pat. No. 4,843,583 which discloses an arrangement employing feedback of a signal to a nonlinear adaptive filter and an adjustable linear filter serially connected thereto. A processor is used to generate intermediate signals and then a second processor is used to obtain a desired output.
There is a need for a method and circuitry (1) capable of handling both positive and negative polarity additive disturbances without preconditioning; (2) capable of handling disturbances with more than one time constant involved in the decay, without requiring a prefilter; and (3) less susceptible to noise and internal circuit offsets than methods and circuitry heretofore proposed.